Miniaturized bioreactor for bioprocessing: design and optimisation of a three-phase fluidized bed

Abstract

The fluidized bed reactor (FBR) is a processing platform relying on the fluidization of solids by liquid/gas flows, thus achieving the excellent multi-phases contact, minimum diffusional resistance, good heat and mass transfer. Recently, the miniaturization of fluidized bed has received much attention due to its fast screening and process intensification. However, the application of miniaturized fluidized bed in bioprocessing and bioproduction is still not explored, although FBR enables higher mass transfer, lower shear force and less energy consumption compared with flask, stirred-tank reactor and photobioreactor, respectively. To broaden the applicability of fluidized bed reactor in bioprocessing, this thesis combined the miniaturized fluidized bed reactor with Nidula niveo-tomentosa fungi to investigate the performance of FBR on fungal fermentation and raspberry ketone bioproduction. Thus, four main research themes were subsequently formulated and explored: (I). Design and fabrication of the micro-fluidized bed through 3D-printing technique; (II). Development of deeper understanding of the micro-fluidized bed based on liquid-gas and liquid-solid-gas hydrodynamic characteristics; (III). Investigation the cultivation parameters and different bioreactors for fungal fermentation and production; (IV). Development and investigation of a bench-scale fluidized bed reactor for fungal fermentation and raspberry ketone production. The preliminary study of pellet fluidization provided an experimental basis for the fungal fermentation using fluidized bed reactor, as fungal pellets in the micro-fluidized bed could be well fluidized by both liquid and gas flows, while the gas flow can not only improve the mixing but also decrease pellet agglomeration. Then, the following study demonstrated that the optimal cultivation conditions including 75g/l glucose concentration, 2.5 g/l of phenylalanine, 3-weekold of 40% seed culture can largely improve raspberry ketone (RK) production in flask culture. Besides, the homogenization which breaks the pellets into free mycelia can further promote ii RK production. Finally, the combination of these optimal parameters with the bench-scale fluidized bed bioreactor yielded raspberry ketone (up to 5 times compared to the control study by flask culture) and raspberry compounds (up to 3 times compared to the control study by flask culture), improving the overall bioproduction of Nidula niveo-tomentosa fungi. Therefore, this thesis successfully proved the novel use of fluidized bed bioreactor for fungal fermentation, as the gas/liquid flows can fluidize the pellets which provide sufficient mass transfer and gas supply. Besides, the gas flow can decrease the pellet agglomeration thus mitigating the dead zone. Such a combination of fluidized bed bioreactor with fungal pellets opens up opportunities to develop a suitable and efficient bioprocessing technique in fungal fermentation.